Total HTML Converter: On Mac some letters are invisible in generated PDF

A customer who loaded a PDF generated with Total HTML ConverterX wrote us: He uses an Apple Mac with OS X 10.6.4
The Mac-Reader "Preview" shows the PDF correctly, but when he prints the document all 'o'-Letters are not printed but leave blanks.
When he opens the stored PDF in Acrobat professional/Mac 8.2.2 or Acrobat Reader the 'o'-Letters are invisible already on the display.

Maybe there is a problem with the embedded fonts? Is such an issue known already?

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